<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>菜鸟教程(runoob.com)</title>
    <style type="text/css">
        canvas {
            border: 1px solid black;
        }
    </style>
</head>
<body>
<canvas id="tutorial" width="300" height="300"></canvas>
<script type="text/javascript">
    function draw(){
        var canvas = document.getElementById('tutorial');
        if(!canvas.getContext) return;
        var ctx = canvas.getContext("2d");
        ctx.fillStyle = "rgb(200,0,0)";
        //绘制矩形
        ctx.fillRect (10, 10, 55, 50);

        ctx.fillStyle = "rgba(0, 0, 200, 0.5)";
        ctx.fillRect (30, 30, 55, 50);
    }
    draw();
</script>
</body>
</html>